The why of seating depth ?
- Thread starter Hal
- Start date
It may affect bullet alignment. It certainly affects both total pressure and probably the shape of the pressure curve.
And in some barrels, it may not affect anything. I have several barrels that shoot very well whatever the seating depth -- hard jam to .020 off, or anything in between. In those, I jam the bullet hard, as Boyd Allen has shown that can (somewhat) straighten a slightly crooked round. One less thing to worry about...
And in some barrels, it may not affect anything. I have several barrels that shoot very well whatever the seating depth -- hard jam to .020 off, or anything in between. In those, I jam the bullet hard, as Boyd Allen has shown that can (somewhat) straighten a slightly crooked round. One less thing to worry about...
Seating depth may also affect (not effect) when the bullet leaves the barrel. If it does, this fits with why group size/shape may change with seating depth changes.....the muzzle may physically be in a different place in it's vibrational pattern as you change seating depths. I've z-e-r-o evidence to back this axiom up. Heck, it's doubtful it could be proven, given the many other variables. I do know that with my barrels that have been properly indexed to either the 12:00 or 6:00 position seem to be less critical to seating depth changes.
All .30 cal. stuff.....I'm clueless about this with the .22's and 6's.
Good shootin'.
-Al
All .30 cal. stuff.....I'm clueless about this with the .22's and 6's.
Good shootin'.
-Al
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fishbone
Guest
What is considered a "hard jam" on 6ppc's, that is if a value can be assigned?
"Hard jam" -- Not a value that can be assigned, and changes from person to person.
However, a "normal" jam, with a typical throat (1.5 degrees half-cone angle) would be marks on the bullet half as long as they are wide. All subject to "typical" land profiles, of course. etc. etc.
Anything giving marks longer than that might be called a hard jam by somebody.
Alternatively, a .005 to .010 "jam" would also be generally thought typical. Actual distance subject to what you call "zero" of course. Any more would start to qualify as a hard jam by somebody...
However, a "normal" jam, with a typical throat (1.5 degrees half-cone angle) would be marks on the bullet half as long as they are wide. All subject to "typical" land profiles, of course. etc. etc.
Anything giving marks longer than that might be called a hard jam by somebody.
Alternatively, a .005 to .010 "jam" would also be generally thought typical. Actual distance subject to what you call "zero" of course. Any more would start to qualify as a hard jam by somebody...
Al, German Salazer determiend to his satisfaction that clocking a barrel gave better and worse groups, and the group position changed on the target. I think he only tested .22 RF, and of course, German makes no claims beyond what he found.
A barrel clocked so the groups were in the 6 o'clock position *usually* gave the best performance. Since you seem to regularly clock your barrels, have you found this to be true in CF? Or is the 12 o'clock position usually just as good?
Charles, at either 6:00 or 12:00 have worked well for me. If I was a long range competition shooter or long range hunter, I'd opt indexing for a bit of 'free' elevation.
As an aside....a BR c.f. action that would allow easy 360 degree barrel indexing could be a huge leap forward.
Good shootin'. -Al
As an aside....a BR c.f. action that would allow easy 360 degree barrel indexing could be a huge leap forward.
Good shootin'. -Al
Al, the notion of "free elevation" has always amused me, That's what tapered bases are for. You're just as apt to need a little more "down" as "up"...
As for the CF benchrest action that allows clocking the barrel with no change in head clearance, Beggs & Stiller described a system that will work. For a 30-BR, you probably need a receiver with a 1-1/8 tenon to make the bushing work.
As for the CF benchrest action that allows clocking the barrel with no change in head clearance, Beggs & Stiller described a system that will work. For a 30-BR, you probably need a receiver with a 1-1/8 tenon to make the bushing work.
Boyd Allen
Active member
Charles,
I disagree (hopefully not too disagreeably) , with what you wrote about the definition of jam. IMO jam is the longest that a particular bullet can be seated, at a particular neck tension, in a particular barrel, without the overall length of the loaded round being decreased as the bolt is being closed during the chambering of the round. (Yes, more than a bit wordy) From this we get the common reference (in benchrest parlance) of someone saying that he is seating some distance off of jam. Unfortunately jammed has been used to mean into the rifling, in some cases, to any degree longer than where the bullet just touches the rifling. I picked up what I think to be the correct definition, decades back, from my earliest reading in Precision Shooting magazine, and I have found most of the in print uses within benchrest writings to be consistent with it. If one prefers to use the point where a bullet just makes contact with the rifling as a starting point I think that it would be better if he would say that his bullets are seated whatever amount longer than touch or touching rather than jammed the same amount. If on the other hand, if one judges the correctness of a definition by how it is most commonly used, the internet has made published writers of the world, and by sheer numbers alone the original meaning may have been out voted down to a lower level on the theoretical list of definitions.
Boyd
I disagree (hopefully not too disagreeably) , with what you wrote about the definition of jam. IMO jam is the longest that a particular bullet can be seated, at a particular neck tension, in a particular barrel, without the overall length of the loaded round being decreased as the bolt is being closed during the chambering of the round. (Yes, more than a bit wordy) From this we get the common reference (in benchrest parlance) of someone saying that he is seating some distance off of jam. Unfortunately jammed has been used to mean into the rifling, in some cases, to any degree longer than where the bullet just touches the rifling. I picked up what I think to be the correct definition, decades back, from my earliest reading in Precision Shooting magazine, and I have found most of the in print uses within benchrest writings to be consistent with it. If one prefers to use the point where a bullet just makes contact with the rifling as a starting point I think that it would be better if he would say that his bullets are seated whatever amount longer than touch or touching rather than jammed the same amount. If on the other hand, if one judges the correctness of a definition by how it is most commonly used, the internet has made published writers of the world, and by sheer numbers alone the original meaning may have been out voted down to a lower level on the theoretical list of definitions.
Boyd
David Halblom
Flying Fish Fundamentals
David, what I'm suggesting is a way to turn the barrel 360 degrees in the reciever without changing the headspace.
Good shootin'. -Al
JerrySharrett
Senile Member
Charles, if you are using the term "clocking" as I think you are then the bore exit location would certainly effect POI. It will also affect gun reaction to recoil and how it performs on the bags. That is why I am so against this Gritters method of barrel alignment for chambering. BTW, DT fully agrees with me, remember his 10 barrel test?
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fishbone
Guest
Thanks Vern, Boyd & Charles..... I use the Hornady device to find 'just touching' and measure from there to record jam (JT + 0.0xx). A powder test yesterday was done with the bullets seated +0.010". With a charge now identified, a test of various seating depths will be next. I was just looking for some jam value, that beyond, would put me in shaky territory.
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fishbone
Guest
Oh? It would seem that 'if used correctly', a good reading could be had.
Chambering a brass/bullet (overlength) to engrave land marks is a more coarse measurement.
I'm learning.
Fishbone,
I had a stoney point tool, the problem lays in the case. Unless you fireform a case three times and then tap it your self, it is impossible for the tool to give a correct reading as the headspace will be wrong. Making a case for every barrel is just to much of a PIA to do all the time. The only measurement you are getting, without making your own cases, is from the shoulder to the lands and what you need is from the casehead to the lands. So basically, your measuring from the shoulder to lands and measuring from the casehead to lands...it just don't work without fitted cases. Chambering a round with a bullet and letting the rifling push the bullet in while it is using the casehead as a base is the only way to achieve what your wanting other than fireforming cases and tapping them. Just think about it a while.
Hovis
I had a stoney point tool, the problem lays in the case. Unless you fireform a case three times and then tap it your self, it is impossible for the tool to give a correct reading as the headspace will be wrong. Making a case for every barrel is just to much of a PIA to do all the time. The only measurement you are getting, without making your own cases, is from the shoulder to the lands and what you need is from the casehead to the lands. So basically, your measuring from the shoulder to lands and measuring from the casehead to lands...it just don't work without fitted cases. Chambering a round with a bullet and letting the rifling push the bullet in while it is using the casehead as a base is the only way to achieve what your wanting other than fireforming cases and tapping them. Just think about it a while.
Hovis